Patent Application
20200230728
The present disclosure relates generally to methods of joining objects, and more particularly to methods of joining ceramic materials and the resulting joined assemblies.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Support pedestals are often used in semiconductor processing. A support pedestal typically includes a plate member for supporting a wafer thereon and a tubular shaft disposed under the plate member. The plate member may include a ceramic substrate and a plurality of functional elements, such as a heating element, embedded in the ceramic substrate.
The ceramic substrate may be formed by hot pressing. Hot pressing is a high-pressure, low-strain process to enhance densification of powder or compacted preform at high temperature. Typically, the powder or the compacted preform is put into a mold, and high temperatures and pressure are applied for densification and sintering.
The functional elements that are embedded in the ceramic substrate must withstand high heat and high pressure in the hot pressing process. Therefore, the materials for forming the functional elements are limited. Moreover, hot pressing requires high temperature and high pressure equipment, thereby increasing manufacturing costs.
In some cases, two or more ceramic substrates may be bonded together by brazing. However, the brazed joint is not without problems due to poor wettability of the ceramic materials as well as the incompatible coefficient of thermal expansion (CTE) between the brazing metals and the ceramic materials. Cracks or delamination may occur between the brazing metals and the ceramic substrates at elevated temperatures due to their significantly different thermal expansions.
These challenges, among other challenges, in manufacturing ceramic support pedestals are addressed by the present disclosure.
In one form of the present disclosure, a method of joining is provided. The method comprises preparing a first member, preparing a second member, and forming at least one trench in at least one of the first member and the second member. The method further comprises placing a strip of solid aluminum material between the first member and the second member across the trench, bringing the first member and the second member together to contact the solid aluminum material and to form an assembly, and applying a force and heat to the assembly above a melting point of the solid aluminum material such that the solid aluminum material flows into the trench. Additionally, the method further includes applying additional heat to the assembly at or above a wetting temperature of the member in which the trench is formed to bond the first member to the second member along adjacent faces and cooling the assembly, wherein a spacing between the first member and the second member along the adjacent faces is less than 5 μm.
In another form of this method, preparing the first and second member comprises creating a surface roughness of the adjacent faces of the first and second members between 5 μm and 100 nanometers.
In yet another form of this method, the first member and the second member are selected from the group consisting of aluminum nitride (AlN), alumina, zirconia, and silicon carbide (SiC).
In at least one form of this method, each of the first member and the second member are each aluminum nitride (AlN). In variations of this method, the wetting temperature is above 850° C.
In other forms of this method, a purity of the strip of solid aluminum material is greater than or equal to about 97% and the assembly is heated to a temperature above about 800° C., and the force applied to the assembly is between about 0.1 MPa to 6.5 MPa.
In another form of this method, applying additional heat to the assembly comprises heating the assembly to 1100° C. under a vacuum condition of approximately 10−3 Torr.
In numerous forms of this method, applying additional heat to the assembly comprises heating the assembly to 800° C. under a vacuum condition of approximately 10−6 Torr.
In at least one form of this method, the solid aluminum material is aluminum foil.
In some forms of this method, the solid aluminum material is applied by a physical vapor deposition (PVD) process.
In still another form of this method, at least one trench is formed with a depth and a width, and the width of the trench is between 5 and 20 times the depth of the trench.
In numerous forms of this method, each of the first member and the second member are each a flat plate.
In a form of this method, the first member is a flat plate and the second member is a hollow shaft.
Other forms of this method further comprise forming a plurality of trenches that are spaced a distance apart less than 2 mm.
In another form of the present disclosure, a method of joining is provided. The method comprises preparing a first member, preparing a second member, and forming a plurality of trenches spaced a distance apart less than 2 mm in at least one of the first member and the second member. The method further comprises placing a strip of solid aluminum material between the first member and the second member across the trench, bringing the first member and the second member together to contact the solid aluminum material and to form an assembly, and applying a force and heat to the assembly above a melting point of the solid aluminum material such that the solid aluminum material flows into the trench. Additionally, the method further comprises applying additional heat to the assembly at or above a wetting temperature of the member in which the trench is formed to bond the first member to the second member along adjacent faces and cooling the assembly, wherein a spacing between the first member and the second member along the adjacent faces is less than 5 μm.
In at least one form of this method, preparing the first and second member comprises creating a surface roughness of the adjacent faces of the first and second members between 5 μm and 100 nanometers.
Additionally, in other forms of this method, the first member and the second member are selected from the group consisting of aluminum nitride (AlN), alumina, zirconia, and silicon carbide (SiC).
In some forms of this method, each of the first member and the second member are each aluminum nitride (AlN).
In yet another form of this method, the solid aluminum material is aluminum foil.
Alternatively, in another form of this method, the solid aluminum material is applied by a physical vapor deposition (PVD) process.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
Referring to
The first and second members 12, 14 in this form each have a plate configuration and define adjacent faces 18 facing each other. In one form, the adjacent faces 18 have a surface flatness of less than 5 μm, and a surface roughness of less than 3 μm. In one application, the surface roughness of the adjacent faces 18 may be in the range between 100 nm and 5 μm. A spacing between the first member 12 and the second member 14 along the adjacent faces is less than 5 μm in one form of the present disclosure.
Referring to
In
When a plurality of trenches 22 are formed, the plurality of trenches 22 may be configured parallel to each other and are spaced at a distance apart less than 2 mm. Making the trenches 22 closer to each other can reduce the size of the bonding area to less than 2 mm. A smaller bonding area has the advantages of reducing the area that needs to be heated to the wetting temperature and achieving uniform heating in the bonding area during the bonding process, which will be described in more detail below. Moreover, the smaller bonding area reduces the risk of aluminum flowing into adjacent area where functional elements such as vias, routing circuits, terminations, among others, are disposed. The trenches 22 are also configured limit the flow of aluminum, or other bonding material that may be used besides aluminum, in the bonding area.
In one form, the number of the trenches 22 is at least three or at least five. The aspect ratio (i.e., the width/depth) of each of the trenches 22 is between 5 to 20. In other words, the width of each trench is between 5 and 20 times the depth of each trench 22. A shallower trench 22 contributes to a desired hermeticity of less than 10−9 mbar-l/sec. The width of the bonding area may be less than 3 mm. The depth of the trenches 22 is less than 50 μm, and in one form less than 20 μm to reduce thermal stress due to differences in thermal expansion between the bonding material (i.e., aluminum) and the ceramic member (i.e., AlN). When a deeper trench (e.g., larger than 100 μm) is used, the trench 22 should be made wider in order to achieve the required hermeticity.
When the first and second members 12, 14 are circular members, the plurality of trenches 22 are configured to have an annular shape along the periphery of the first and second members 12, 14. However, the shape (or path) of the trenches 22 may vary according to application requirements and may further be of a varying width (rather than a constant width as illustrated herein) while remaining within the scope of the present disclosure.
Referring now to
Next, at least one trench 22 is formed in the adjacent face 18 of at least one of the first and second members 12, 14 in step 54. Referring to
Thereafter, force and heat is applied to the assembly of the first and second members 12, 14 and the solid aluminum material above a melting point of the solid aluminum material in step 58. The melting point of the solid aluminum material is approximately 660° C. The force is applied on the first and second members 12, 14 to press the first and second members against each other. In this step, the solid aluminum material is melted and the molten aluminum material flows into the trenches 22 as shown in
The heat can be applied locally to the bonding area of the first and second members 12, 14 to reduce the risks of damaging the functional elements disposed at other areas of the first and second members 12, 14.
Next, additional heat is applied to the assembly at or above a wetting temperature of the first member 12 or second member 14 where the trench 22 is formed to bond the first member 12 to the second member 14 along adjacent faces 18 in step 60. For aluminum nitride, the wetting temperature is above 850° C. In this step, alumina native oxide is broken in order to achieve wettability of the ceramic material. Wettability of the ceramics can be achieved when a purity of aluminum is greater than or equal to about 97%, the temperature is above about 800° C., the pressure is about 0.1 MPa to 6.5 MPa and a vacuum condition is approximately 10−3 Torr and below a vacuum level. Vacuum level and temperature are balanced to achieve wettability according to the teachings of the present disclosure. Wettability can be achieved at 10−3 Torr and at temperature of 1100° C., or at 10−6 Torr and at a temperature of 800° C. When the thermal process is performed between 1 to 10 hours, the aluminum begins to diffuse into the aluminum nitride to conform to the geometry of the aluminum nitride. Therefore, the molten aluminum material is shaped to conform to the geometry of the trenches 22 as shown in
Similarly, the additional heat can be applied locally to the bonding area, rather than the entire assembly, to reduce the risks of damaging the functional elements disposed at other areas of the first and second members 12, 14.
As shown in
After the first member 12 is bonded to the second member 14, the assembly is cooled in step 62.
Referring to
Referring to
It should be understood that the trenches may take on any shape other than those illustrated herein, including by way of example, tapered (inwardly or outwardly), dovetail, or polygonal, among other shapes. Also, the “width” of the trench as used and claimed herein refers to the maximum dimension across the trench for any given geometrical shape of the trench, such as the arcuate shape in
With the bonding method of the present disclosure, ceramic materials can be relatively easily bonded. This method can be used to manufacture a ceramic pedestal in semiconductor processing, however, other applications are contemplated according to the teachings of the present disclosure. Therefore, the various functional layers may be formed on a plurality of ceramic members and then joined together by aluminum materials to form the heating plate. Accordingly, high temperature and high pressure equipment for a hot pressing operation may not be needed to form a monolith substrate, thereby reducing the manufacturing costs.
Moreover, the bonding methods according to the present disclosure involve relatively lower temperatures and relatively lower pressures. As a result, a wider selection of materials is available for forming the various functional layers in the ceramic substrate. For example, a layered heater formed by a thick film, thin film, thermal spray, or sol-gel process may be applied on one of the first and second members before the first and second members are bonded together using the bonding method of the present disclosure. TiNiHf termination braze, Nickel termination plating, or Aremco® anchor paste may be applied on the first member and/or the second member before the first and second members are bonded using the method of the present disclosure.
The bonding methods can also be used to bond a heating plate to a tubular shaft of the support pedestal to provide thermocouple pocket isolation. The bonding method can be used to manufacture a thin (thickness between 10 and 50 mm) flat (surface roughness less than 10 μm) AlN heater assembly in a variety of applications including AlN electrostatic chuck assembly.
Further, a support pedestal manufactured by the bonding methods of the present disclosure allows for repair and replacement of the heating plate, thereby increasing the life of the support pedestal.
It should be noted that the disclosure is not limited to the form described and illustrated as examples. A large variety of modifications have been described and more are part of the knowledge of the person skilled in the art. These and further modifications as well as any replacement by technical equivalents may be added to the description and figures, without leaving the scope of the protection of the disclosure and of the present patent.
This application is a divisional of U.S. application Ser. No. 15/955,431, filed on Apr. 17, 2018. The disclosure of the above application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15955431 | Apr 2018 | US |
| Child | 16805952 | US |
